1. Field of the Invention
The present invention relates to a sheet conveying device and a control method therefor, and more particularly to a sheet conveying device that conveys sheets using lots of conveying roller pairs and a method of controlling the sheet conveying device.
2. Description of the Related Art
Conventionally, in an image forming apparatus, such as a printer or a multifunction machine, a sheet for printing (for image formation) is conveyed using lots of conveying rollers. Each of these conveying rollers is comprised of a pair of a driving roller driven to rotate by a motor and a driven roller for pressing a sheet against the driving roller. A sheet is nipped between the driving roller driven to rotate and the driven roller in each of the conveying roller pairs and is passed from one roller pair to another. Thus, the sheet is conveyed.
In a sheet conveying mechanism configured as above, in the case of concurrently nipping one sheet by a plurality of roller pairs, it is required to match a sheet conveying speed between the roller pairs for concurrently nipping the sheet. In general, this control for matching the sheet conveying speed is performed by controlling the rotational speed of each driving roller. However, variation in the roller diameters of the respective driving rollers and mounting tolerance thereof can make the actual sheet conveying speed different between an upstream driving roller and a downstream driving roller concurrently nipping a sheet.
To solve this problem, there has been proposed a device provided with a correction means for detecting an error amount between the conveying speed of a driving roller and a target speed, and correcting the conveying speed based on the detected error amount (see Japanese Patent Laid-Open Publication No. H03-002068).
However, even if conveying speed information is corrected as disclosed in Japanese Patent Laid-Open Publication No. H03-002068, it is difficult to obtain a perfect match between the conveying speed of an upstream conveying roller pair and that of a downstream conveying roller pair. This sometimes causes a trouble, such as the loss of synchronization of motors for driving respective conveying roller pairs, particularly depending on the type (characteristic) of sheets.